1. Technical Field
The present disclosure relates to nonaqueous electrolytic solutions for nonaqueous electrolyte secondary batteries and to nonaqueous electrolyte secondary batteries.
2. Description of the Related Art
A nonaqueous electrolytic solution used in nonaqueous electrolyte secondary batteries includes a nonaqueous solvent and an electrolyte salt. Non-Patent Literature 1 (ECS Transactions, 11 (29) 91-98 (2008), Electrolytes Containing Fluorinated Ester Co-Solvents for Low-Temperature Li-Ion Cells) discloses that the use of a nonaqueous solvent which includes a fluorinated carboxylate ester provides good low-temperature discharge characteristics. Further, Patent Literature 1 (Japanese Patent No. 5235437) discloses that high-temperature storage characteristics are improved by using a nonaqueous solvent which includes a fluorinated carboxylate ester having a hydrogen atom at the α-position.
In the techniques disclosed in Non-Patent Literature 1 and Patent Literature 1, the fluorinated carboxylate ester is decomposed by an alkali component present in the positive electrode during the first charging and the decomposition product is diffused toward the negative electrode to form an excessively thick film. The film inhibits the deintercalation of lithium ions from the negative electrode during discharging to cause a decrease in initial efficiency. In particular, the decrease in initial efficiency is marked in the case of a Ni-rich positive electrode active material because the active material contains a large amount of an alkali component.